US7522696B2 - X-ray CT apparatus - Google Patents
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- US7522696B2 US7522696B2 US11/620,627 US62062707A US7522696B2 US 7522696 B2 US7522696 B2 US 7522696B2 US 62062707 A US62062707 A US 62062707A US 7522696 B2 US7522696 B2 US 7522696B2
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
- A61B6/032—Transmission computed tomography [CT]
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/03—Computerised tomographs
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/02—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
- A61B6/027—Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis characterised by the use of a particular data acquisition trajectory, e.g. helical or spiral
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/48—Diagnostic techniques
- A61B6/481—Diagnostic techniques involving the use of contrast agents
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/50—Clinical applications
- A61B6/504—Clinical applications involving diagnosis of blood vessels, e.g. by angiography
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/54—Control of apparatus or devices for radiation diagnosis
- A61B6/541—Control of apparatus or devices for radiation diagnosis involving acquisition triggered by a physiological signal
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
- G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
- G01N23/046—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material using tomography, e.g. computed tomography [CT]
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/24—Detecting, measuring or recording bioelectric or biomagnetic signals of the body or parts thereof
- A61B5/316—Modalities, i.e. specific diagnostic methods
- A61B5/318—Heart-related electrical modalities, e.g. electrocardiography [ECG]
- A61B5/346—Analysis of electrocardiograms
- A61B5/349—Detecting specific parameters of the electrocardiograph cycle
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/72—Signal processing specially adapted for physiological signals or for diagnostic purposes
- A61B5/7203—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal
- A61B5/7207—Signal processing specially adapted for physiological signals or for diagnostic purposes for noise prevention, reduction or removal of noise induced by motion artifacts
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B6/00—Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
- A61B6/50—Clinical applications
- A61B6/503—Clinical applications involving diagnosis of heart
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2223/00—Investigating materials by wave or particle radiation
- G01N2223/40—Imaging
- G01N2223/419—Imaging computed tomograph
Definitions
- the present invention relates to an X-ray CT apparatus or a technique for an X-ray CT image photographing or imaging method, which realize cardiac imaging or biological synchronous imaging based on low radiation exposure, high image quality and high-speed photography by an electrocardiographically-synchronized helical scan, variable-pitch helical scan or helical shuttle scan at a medical X-ray CT (Computed Tomography) apparatus.
- X-ray CT Computed Tomography
- the present imaging method involves a problem in terms of X-ray exposure because of the low helical pitch.
- Data acquisition in which one segment is defined as fan angles+180° is shown in FIG. 16 .
- Patent Document 1 Japanese Unexamined Patent Publication No. 2003-164446
- an object of the present invention is to provide an X-ray CT apparatus capable of realizing the photography or imaging of a heart at a low dosage and a high speed and with good image quality by a helical scan, variable pitch helical scan or helical shuttle scan of the X-ray CT apparatus having a multi-row X-ray detector or a two-dimensional X-ray area detector of matrix structure typified by a flat panel X-ray detector.
- the present invention provides an X-ray CT apparatus including an X-ray data acquisition device for acquiring X-ray projection data transmitted through a subject lying between an X-ray generator and an X-ray detector having a two-dimensional detection plane and detecting X rays in opposition to the X-ray generator, while the X-ray generator and the X-ray detector are being rotated about a center of rotation lying therebetween; an image reconstructing device for image-reconstructing the acquired projection data; an image display device for displaying the image-reconstructed tomographic image; and an imaging condition setting device for setting various kinds of imaging conditions for tomographic image, wherein the X-ray data acquisition device acquires X-ray projection data in sync with an external sync signal by a helical scan with a predetermined range of the subject with a helical pitch set to 1 or more.
- the present invention provides an X-ray CT apparatus including an X-ray data acquisition device for acquiring X-ray projection data transmitted through a subject lying between an X-ray generator and an X-ray deter having a two-dimensional detection plane and detecting X rays in opposition to the X-ray generator, while the X-ray generator and the X-ray deter are being rotated about the center of rotation lying therebetween; an image reconstructing device for image-reconstructing the acquired projection data; an image display device for displaying the image-reconstructed tomographic image; and an imaging condition setting device for setting various imaging conditions for a tomographic image, wherein the X-ray data acquisition device performs X-ray data acquisition with a timing at which a predetermined imaging position in a z direction that is a relative travel direction between the subject and an X-ray data acquisition system including the X-ray generator and the X-ray detector is synchronized with a predetermined phase of an external sync signal, upon imaging a predetermined range of the subject by
- the present invention provides an X-ray CT apparatus including an X-ray data acquisition device for acquiring X-ray projection data transmitted through a subject lying between an X-ray generator and an X-ray detector having a two-dimensional detection plane and detecting X-rays in opposition to the X-ray generator, while the X-ray generator and the X-ray detector are being rotated about a center of rotation lying therebetween; an image reconstructing device for image-reconstructing the acquired projection data; an image display device for displaying the image-reconstructed tomographic image; and an imaging condition setting device for setting various kinds of imaging conditions for tomographic image, wherein the X-ray data acquisition device includes a first X-ray data acquisition device for performing first X-ray data acquisition based on a first imaging condition defined in such a manner that a predetermined imaging position in a z direction that is a relative travel direction between the subject and an X-ray data acquisition system including the X-ray generator and the X-ray detector is synchronized with
- FIG. 1 is a block diagram showing an X-ray CT apparatus according to one embodiment of the present invention
- FIG. 2 is an explanatory diagram of an X-ray generator (X-ray tube) and a multi-row X-ray detector as viewed in an xy plane.
- FIG. 3 is an explanatory diagram of the X-ray generator and the multi-row X-ray detector as viewed in a yz plane.
- FIG. 4 is a flowchart illustrating the flow of subject photography.
- FIG. 5 is a flowchart showing a schematic operation for image reconstruction, of the X-ray CT apparatus according to the one embodiment of the present invention.
- FIG. 6 is a flowchart depicting the details of a pre-process.
- FIG. 7 is a flowchart illustrating the details of a three-dimensional image reconstructing process.
- FIG. 8 is a conceptual diagram showing a state in which lines on an image reconstruction area are projected in an X-ray penetration direction.
- FIG. 9 is a conceptual diagram illustrating lines projected onto an X-ray detector plane.
- FIG. 10 is a conceptual diagram showing a state in which projection data Dr (view, x, y) is projected onto an image reconstruction area.
- FIG. 11 is a conceptual diagram illustrating backprojection pixel data D 2 of respective pixels on an image reconstruction area.
- FIG. 12 is an explanatory diagram depicting a state in which backprojection pixel data D 2 are added together over all views in association with pixels to obtain backprojection data D 3 .
- FIG. 13 is a conceptual diagram showing a state in which lines on a circular image reconstruction area are projected in an X-ray penetration direction.
- FIG. 14 is a diagram illustrating an imaging or photographing condition input screen of the X-ray CT apparatus.
- FIG. 15 is a diagram depicting examples of a volume rendering three-dimensional image display method, an MPR image display method and a three-dimensional MIP image display method.
- FIG. 16 is an explanatory diagram showing helical scan half scan (180°+fan angle) image reconstruction of one segment synchronized with a biological signal.
- FIG. 17 is an explanatory diagram illustrating helical half scan (180°+fan angles) image reconstruction divided into three segments.
- FIG. 18 is an explanatory diagram depicting helical full scan (360°) image reconstruction divided into four segments.
- FIG. 19 is a diagram showing weighted addition of projection data on respective segments.
- FIG. 20 is a diagram illustrating band artifacts at a cardiac three-dimensional display.
- FIG. 21 is a flowchart illustrating conventional cardiac photography
- FIG. 22( a ) is a diagram showing the waveform of an electrocardiographic signal of a subject.
- FIG. 22( b ) is a diagram illustrating a sync signal based on a cardiac phase.
- FIG. 22( c ) is a diagram depicting a sync signal based on a cardiac triggered phase.
- FIG. 23 is a flowchart of a first embodiment.
- FIG. 24 is a diagram showing a mesodiastolic cardiac coronal image.
- FIG. 25 is a diagram showing the relationship between a helical scan at an actual scan and a cardiac periodic signal.
- FIG. 26 is a diagram illustrating the relationship between a helical scan at an actual scan and a cardiac periodic signal where a cardiac period is made long.
- FIG. 27 is a diagram showing the relationship between a helical scan at an actual scan and a cardiac periodic signal where a cardiac period is made short.
- FIG. 28 is a diagram depicting the flow of a contrast agent synchronous imaging process.
- FIG. 29 is a diagram showing an intermittent scan for a monitor scan
- FIG. 30( a ) is a diagram illustrating a baseline tomographic image.
- FIG. 30( b ) is a diagram showing a display example of a monitor scan for contrast agent synchronous photography.
- FIG. 1 is a configuration block diagram showing an X-ray CT apparatus according to one embodiment of the present invention.
- the X-ray CT apparatus 100 is equipped with an operation console 1 , an imaging or photographing table 10 and a scan gantry 20 .
- the operation console 1 includes an input device 2 which accepts an input from an operator, a central processing unit 3 which executes a pre-process, an image reconstructing process, a post-process, etc., a data acquisition buffer 5 which acquires or collects X-ray detector data acquired by the scan gantry 20 , a monitor 6 which displays a tomographic image image-reconstructed from projection data obtained by pre-processing the X-ray detector data, and a storage device 7 which stores programs, X-ray detector data, projection data and X-ray tomographic images therein.
- FIG. 14 shows an example of an imaging condition input screen.
- An input button 13 a for performing a predetermined input is displayed on the imaging condition input screen 13 A.
- FIG. 14 illustrates a screen on which a scan tab is being selected. When P-Recon is selected as the tab, an input display is switched as plotted below FIG. 14 .
- a tomographic image 13 b is displayed above the input button 13 a and a reconstruction area 13 c is displayed down below.
- Biological signals such as a respiratory signal, an electrocardiographic signal, etc. may be displayed as displayed on the upper right side if necessary.
- the photographing table 10 includes a cradle 12 that draws and inserts a subject from and into a bore or aperture of the scan gantry 20 with the subject placed thereon.
- the cradle 12 is elevated and moved linearly on the photographing table by a motor built in the photographing table 10 .
- the scan gantry 20 includes an X-ray tube 21 , an X-ray controller 22 , a collimator 23 , a beam forming X-ray filter 28 , a multi-row X-ray detector 24 , a data acquisition system (DAS) 25 , a rotating section controller 26 which controls the X-ray tube 21 or the like rotated about a body axis of the subject, and a control controller 29 which swaps control signals or the like with the operation console 1 and the photographing table 10 .
- DAS data acquisition system
- the beam forming X-ray filter 28 is an X-ray filter configured so as to be thinnest in thickness as viewed in the direction of X rays directed to the center of rotation corresponding to the center of imaging, to increase in thickness toward its peripheral portion and to be able to further absorb the X rays. Therefore, the body surface of the subject whose sectional shape is nearly circular or elliptic can be less exposed to radiation.
- the scan gantry 20 can be tiled about ⁇ 30° or so forward and rearward as viewed in a z direction by a scan gantry tilt controller 27 .
- the X-ray tube 21 and the multi-row X-ray detector 24 are rotated about the center of rotation IC.
- the vertical direction is a y direction
- the horizontal direction is an x direction
- the travel direction of each of the table and cradle orthogonal to these is a z direction
- the plane at which the X-ray tube 21 and the multi-row X-ray detector 24 are rotated is an xy plane.
- the direction in which the cradle 12 is moved corresponds to the z direction.
- An electrocardiograph 31 inputs an electrocardiographic signal of the subject therein.
- the waveform of the electrocardiographic signal is generally represented as shown in FIG. 22( a ). Assuming that a cardiac or heart rate is 75 bpm (beat per minute), a cardiac cycle or period becomes 0.8 seconds and such electrocardiographic waveforms (P wave, QRS wave, T wave and U wave) as shown in the drawing appear within this period.
- the cardiac atria excites and cont with the timing of the P wave, thereby allowing bloodstream from each of a large vein and a pulmonary vein to flows into the ventricular side.
- FIG. 2 is a diagram showing a geometrical arrangement or layout of the X-ray tube 21 and the multi-row X-ray detector 24 as viewed from the xy plane.
- FIG. 3 is a diagram showing a geometrical arrangement or layout of the X-ray tube 21 and the multi-row X-ray detector 24 as viewed from a yz direction.
- the X-ray tube 21 generates an X-ray beam called a cone beam CB.
- the direction of a central axis of the cone beam CB is parallel to the y direction, this is defined as a view angle 0°.
- the multi-row X-ray detector 24 has X-ray detector rows corresponding to J rows, for example, 256 rows as viewed in the z direction.
- Each of the X-ray detector rows has X-ray detector channels corresponding to I channels, for example, 1024 channels as viewed in a channel direction.
- an X-ray beam emitted from the X-ray focal point of the X-ray tube 21 is set such that more X rays are irradiated at the center of a reconstruction area P by the beam forming X-ray filter 28 and less X rays are irradiated at a peripheral portion thereof thereby.
- the X rays are absorbed into a subject existing inside the reconstruction area P, and the penetrated X rays are acquired or collected by the multi-row X-ray detector 24 as X-ray detector data.
- the X-ray beam emitted from the X-ray focal point of the X-ray tube 21 is controlled in the direction of slice thickness of a tomographic image by the X-ray collimator 23 . That is, the X-ray beam is controlled in such a manner that an X-ray beam width becomes D at the center or central axis of rotation IC.
- the X-rays are absorbed into the subject existing in the neighborhood of the central axis of rotation IC, and the penetrated X-rays are acquired by the multi-row X-ray detector 24 as X-ray detector data
- the X-rays are applied to the subject and acquired projection data are A/D converted by the data acquisition system (DAS) 25 from the multi-row X-ray detector 24 , which in turn are inputted to the data acquisition buffer 5 via a slip ring 30 .
- the data inputted to the data acquisition buffer 5 are processed by the central processing unit 3 in accordance with the corresponding program stored in the storage device 7 , so that the data are image-reconstructed as a tomographic image, followed by being displayed on the monitor 6 .
- multi-row X-ray detector 24 is applied in the present embodiment, a two-dimensional X-ray area detector of a matrix structure typified by a flat panel X-ray detector can also be applied, or a one-row type X-ray detector can be applied.
- FIG. 4 is a flowchart showing the rough outline of operation of the X-ray CT apparatus according to the present embodiment.
- Step P 1 a subject is placed on its corresponding cradle 12 and their alignment is performed.
- a slice light central position of the scan gantry 20 is aligned with a reference point of its each portion or region.
- scout image (called also “scano image or X-ray penetrated image”) acquisition is performed.
- the scout image can be normally imaged or photographed at 0° and 90°. Only the 90° scout image might be taken depending upon the region as in the case of a head, for example.
- the operation of fixing the X-ray tube 21 and the multi-row X-ray detector 24 and effecting data acquisition of X-ray detector data while the cradle 12 is being linearly moved, is performed upon scout image photography. The details of the photography of the scout image will be explained later in FIG. 5 .
- an imaging condition setting is performed while the position and size of a tomographic image to be photographed on the scout image is being displayed.
- the present embodiment has a plurality of scan patterns such as a conventional scan (axial scan), a helical scan, a variable pitch helical scan, a helical shuttle scan, etc.
- the conventional scan is a scan method of rotating the X-ray tube 21 and the multi-row X-ray detector 24 each time the cradle 12 is moved at predetermined intervals in a z-axis direction, thereby acquiring projection data.
- the helical scan is an photographing or imaging method of moving the cradle 12 at a constant speed while the data acquisition system constituted of the X-ray tube 21 and the multi-row X-ray detector 24 is being rotated, thereby acquiring projection data.
- the variable pitch helical scan is an imaging method of varying the speed or velocity of the cradle 12 while the data acquisition system constituted of the X-ray tube 21 and the multi-row X-ray detector 24 is being rotated in a manner similar to the helical scan, thereby acquiring projection data.
- the helical shuttle scan is a scan method of accelerating/decelerating the cradle 12 while the data acquisition system constituted of the X-ray tube 21 and the multi-row X-ray detector 24 is being rotated in a manner similar to the helical scan, thereby to reciprocate it in the positive or negative direction of a z axis to acquire projection data.
- These plural veins are set information about the whole X-ray dosage corresponding to one time is displayed.
- the number of rotations or time is inputted upon a cine scan, information about X-ray dosage corresponding to the inputted number of rotations or time at its region of interest is displayed.
- Step P 4 a tomographic image is photographed.
- the details of the tomographic image photography and its image reconstruction will be explained later in FIG. 5 .
- Step P 5 the image-reconstructed tomographic image is displayed.
- Step P 6 a three-dimensional image display is performed as shown in FIG. 15 using a tomographic image continuously photographed in the z direction as a three-dimensional image.
- a volume rendering three-dimensional image display method 40 As three-dimensional image display methods, a volume rendering three-dimensional image display method 40 , a three-dimensional MIP (Maximum Intensity Projection) image display method 41 , an MPR (Multi Plain Reformat) image display method 42 and a three-dimensional reprojection image display method are shown in FIG. 15 .
- the various image display methods can be used properly according to diagnostic applications.
- FIG. 5 is a flowchart showing rough outlines of operations for the tomographic image photography and scout image photography of the X-ray CT apparatus 100 of the present invention.
- Step S 1 the operation of rotating the X-ray tube 21 and the multi-row X-ray detector 24 about the subject and effecting data acquisition of X-ray detector data while the cradle 12 placed on the imaging or photographing table 10 is being linearly moved, is performed upon a helical scan.
- the z-direction coordinate position may be added to X-ray projection data or may be used in association with the X-ray projection data as another file.
- Information about the z-direction coordinate position is used where the X-ray projection data is three-dimensionally image-reconstructed upon the helical shuttle scan and the variable pitch helical scan. Using the same upon the helical scan, conventional scan (axial scan) or cine scan, an improvement in the accuracy of an image-reconstructed tomographic image and an improvement in its quality n be also realized
- position control data on the cradle 12 placed on the photographing table 10 may be used.
- z direction coordinate positions at respective times which are predicted from the imaging operation set upon the imaging condition setting, may also be used.
- variable helical scan or helical shuttle scan data acquisition will be carried out even at acceleration and deceleration in addition to the data acquisition for the range at the constant speed.
- the data acquisition system Upon the conventional scan (axial scan) or the cine scan, the data acquisition system is rotated once or plural times while the cradle 12 placed on the photographing table 10 is being fixed to a given z-direction position, thereby to perform data acquisition of X-ray detector data.
- the cradle 12 is moved to the next z direction position as needed and thereafter the data acquisition system is rotated once or plural times again to perform data acquisition of X-ray detector data.
- a pre-process is performed on the X-ray detector data DO(view, j, i) to convert it into projection data.
- FIG. 6 shows a specific process about the pre-process at Step S 2 .
- an offset correction is performed.
- a logarithmic translation is performed.
- an X-ray dosage correction is performed.
- a sensitivity correction is performed.
- the pre-processed X-ray detector data is completed as a scout image if a pixel size as viewed in the channel direction and a pixel size as viewed in the z direction corresponding to the linear traveling direction of the cradle 12 are displayed in match with the display pixel size of the monitor 6 .
- a beam hardening correction is effected on the pre-processed projection data D 1 (view, j, i) at Step S 3 .
- projection data subjected to the sensitivity correction of Step S 24 of the pre-process S 2 is defined as D 1 (view, j, i) and data subsequent to the beam hardening correction of Step S 3 is defined as D 11 (view, j, i)
- the beam hardening correction of Step S 3 is expressed in the form of, for example, a polynomial as shown below (Equation 1).
- a multiplication operation or computation is expressed in “•” in the present embodiment.
- Step S 4 a z-filter convolution process for applying filters in the z direction (row direction) is effected on the projection data D 11 (view, j, i) subjected to the beam hardening correction.
- the corrected detector data D 12 (view, j, i) is expressed as follows (given by the following equation 4):
- slice thicknesses can be controlled depending upon the distance from an image reconstruction center.
- its peripheral portion In a tomographic image, its peripheral portion generally becomes thick in slice thickness than the reconstruction center thereof. Therefore, the row-direction filter coefficients are changed at the central and peripheral portions so that the slice thicknesses can also be made uniform even at the peripheral portion and the image reconstruction center.
- the row-direction filter coefficients are changed at the central and peripheral portions, the row-direction filter coefficients are changed extensively in width in the neighborhood of a central channel, and the row-direction filter coefficients are changed narrowly in width in the neighborhood of a peripheral channel, each slice thickness can be made approximately uniform even at the peripheral portion and image reconstruction central portion.
- each slice thickness can also be controlled at the central and peripheral portions. Slightly thickening the slice thickness by the row-direction filters provides a great improvement in both artifact and noise. Thus, the degree of an improvement in artifact and the degree of an improvement in noise can also be controlled. That is, the three-dimensionally image-reconstructed tomographic image, i.e., the image quality in the xy plane can be controlled.
- a tomographic image having a thin slice thickness can also be realized by subjecting the row-direction (z-direction) filter coefficients to deconvolution filters.
- a reconstruction function convolution process is performed. That is, projection data is subjected to Fourier transformation for performing transformation into a frequency domain or region and multiplied by a reconstruction function, followed by being subjected to inverse Fourier transformation.
- D 12 projection data subsequent to the z filter convolution process
- D 13 projection data subsequent to the reconstruction function convolution process
- Kernel(j) the convoluting reconstruction function
- the reconstruction function convolution process is expressed as follows (Equation 7).
- the reconstruction function kernel (j) can perform reconstruction function convolution processes independent of one another for every j row of detector, the difference between noise characteristics set for every row and the difference between resolution characteristics can be corrected.
- a three-dimensional backprojection process is effected on the projection data D 13 (view, j, i) subjected to the reconstruction function convolution process to determine backprojection data D 3 (x, y, z).
- An image to be image-reconstructed is three dimensionally image-reconstructed on a plane, i.e., an xy plane orthogonal to the z axis.
- a reconstruction area or plane P to be shown below is assumed to be parallel to the xy plane. The three-dimensional backprojection process will be explained later referring to FIG. 5 .
- Step S 7 a post-process including image filter convolution, CT value conversion and the like is effected on the backprojection data D 3 (x, y, z) to obtain a tomographic image D 31 (x, y, z).
- An image space z-direction filter convolution process shown below may be carried out after the two-dimensional image filter convolution process.
- This image space z-direction filter convolution process may be performed before the two-dimensional image filter convolution process.
- a three-dimensional image filter convolution process may be performed to produce such an effect as to share both of the two-dimensional image filter convolution process and the image space z direction filter convolution process.
- Equation 9 a tomographic image subjected to the image space z-direction filter convolution process is defined as D 33 (x, y, z) and a tomographic image subjected to the two-dimensional image filter convolution process is defined as D 32 (x, y, z)
- equation (Equation 9) is established as follows.
- v(i) is expressed in the form of such a coefficient row as shown below (Equation 10).
- the image space filter coefficient v(i) may be an image space z-direction filter coefficient independent upon the z-direction position.
- the image space z-direction filter coefficient v(i) may preferably use an image space z-direction filter coefficient that depends upon the position of each X-ray detector row in the z direction. This is because it is further effective since detailed adjustments dependent on the row position of each tomographic image can be made.
- the resultant tomographic image is displayed on the monitor 6 .
- FIG. 7 shows the details of Step S 6 in FIG. 5 and is a flowchart showing the three-dimensional backprojection process.
- an image to be image-reconstructed is three-dimensionally image-reconstructed on a plane, i.e., an xy plane orthogonal to the z axis.
- the following reconstruction area P is assumed to be parallel to the xy plane.
- Step S 61 attention is paid to one of all views (i.e., views corresponding to 360° or views corresponding to “180°+fan angles”) necessary for image reconstruction of each tomographic image.
- Projection data Dr corresponding to respective pixels in the reconstruction area P are extracted.
- FIGS. 8( a ) and 8 ( b ) are conceptual diagrams showing the projection of lines on a reconstruction area in an X-ray penetration direction, wherein FIG. 8( a ) shows an xy plan and FIG. 8( b ) shows a yz plane.
- FIG. 9 is a conceptual diagram showing the respective lines in an image reconstruction plane, which are projected onto an X-ray detector plane.
- a square area of 512 ⁇ 512 pixels, which is parallel to the xy plane, is assumed to be a reconstruction area P.
- projection data on lines T 0 through T 511 shown in FIG. 9 obtained by projecting the pixel rows L 0 through L 511 onto the plane of the multi-row X-ray detector 24 in an X-ray penetration direction are extracted, then they result in projection data Dr(view, x, y) of the pixel lows L 0 through L 511 .
- x and y correspond to the respective pixels (x, y) of the tomographic image.
- the X-ray penetration direction is determined depending on geometrical positions of the X-ray focal point of the X-ray tube 21 , the respective pixels and the multi-row X-ray detector 24 . Since, however, the z coordinates z(view) of X-ray detector data D 0 (view, j, i) are known with being added to the X-ray detector data as a table linear movement z-direction position Ztable(view), the X-ray penetration direction can be accurately determined within the X-ray focal point and the data acquisition geometrical system of the multi-row X-ray detector even in the case of the X-ray detector data D 0 (view, j, i) placed under acceleration and deceleration.
- the corresponding projection data Dr(view, x, y) is set to “0”.
- the corresponding projection data Dr(view, x, y) is determined as extrapolation.
- the projection data Dr(view, x, y) corresponding to the respective pixels of the reconstruction area P can be extracted as shown in FIG. 10 .
- Step S 62 the projection data Dr(view, x, y) are multiplied by a cone beam reconstruction weight coefficient to create projection data D 2 (view, x, y) as shown in FIG. 11 .
- the cone beam reconstruction weight coefficient w(i, j) is as follows.
- D 2 ( 0 ,x,y)_a indicates backprojection data for the view ⁇ a
- D 2 ( 0 ,x,y)_b indicates backprojection data for the view ⁇ b
- the cone beam reconstruction weight coefficients ⁇ a and ⁇ b can make use of ones obtained by the following equations.
- ga indicates a weight coefficient of the view ⁇ a
- gb indicates a weight coefficient of the view ⁇ b, respectively.
- Equation 21 max[0, ⁇ ( ⁇ /2+ ⁇ max) ⁇
- each pixel on the reconstruction area P is for multiplied by a distance coefficient.
- the distance coefficient is given as (r 1 /f 0 )2.
- each pixel on the reconstruction area P may be multiplied by the cone beam reconstruction weight coefficient w(i, j) alone,
- the projection data D 2 (view, x, y) is added to its corresponding backprojection data D 3 (x, y) cleared in advance in association with each pixel.
- FIG. 12 shows the concept that the projection data D 2 (view, x, y) is added for every pixel
- Step S 64 Steps S 61 through S 63 are repeated with resect to all views (i.e., views corresponding to 360° or views corresponding to “180°+fan angles”) necessary for image reconstruction of each tomographic image. Adding all the views necessary for the image reconstruction makes it possible to obtain backprojection data D 3 (x, y) shown in the left drawing of FIG. 12 .
- FIGS. 13( a ) and 13 ( b ) are respectively conceptual diagrams each showing a state in which lines on a circular image reconstruction area are projected in an X-ray penetration direction, wherein FIG. 13( a ) shows an xy plane, and FIG. 13( b ) shows a yz plane.
- the reconstruction area P may be set as a circular area whose diameter is 512 pixels, without setting it as the square area of 512 ⁇ 512 pixels.
- An embodiment illustrative of a heart imaging method capable of performing imaging with good quality at a high speed under low exposure using the X-ray CT apparatus is shown below.
- a first embodiment shows an embodiment wherein the appropriateness of the phase of an electrocardiographic signal is determined in advance by a high-speed helical scan large in helical pitch at low X-ray dosage and thereafter a helical scan for an actual scan is performed by means of test injection or contrast agent synchronous photography.
- a second embodiment shows an embodiment related to a method of contrast agent synchronous photography or imaging.
- the first embodiment illustrates the embodiment wherein the appropriateness of the phase of the electrocardiographic signal is determined in advance by the high-speed helical scan large in helical pitch at low X-ray dosage and thereafter the helical scan for the actual scan is performed by means of test injection or contrast agent synchronous photography.
- FIGS. 16 , 17 , 18 and 19 are respectively diagrams for describing the prior art and respectively show the image of the conventional heart imaging process. So-called electrocardiographic synchronous photography or imaging synchronized with the heartbeat has heretofore been performed upon photography of a cardiac coronary r or the like.
- FIG. 22( a ) shows a general electrocardiographic signal.
- the heart rate is 75 bmp (beat per minute)
- a cardiac period becomes 0.8 seconds and such electrocardiographic waveforms (P wave, QRS wave, T wave and U wave) as shown in the drawing appear in this period.
- P wave, QRS wave, T wave and U wave electrocardiographic waveforms
- the flow of the conventional heart imaging method is shown in FIG. 21 .
- Step C 1 a scout scan is performed.
- Step C 2 a low-dosage and fast-helical pitch helical scan (with no contrast agent) for determining a scan range is performed.
- Step C 3 test injection imaging or photography by an intermittent conventional scan (axial scan) at a low dosage is carried out.
- Step C 4 an electrocardiographically synchronized helical scan (used upon contrast) slow in helical pitch is performed.
- Step C 5 an electrocardiographically synchronized helical scan image display is performed.
- the cardiac imaging has heretofore bee carried out in this way.
- the helical scan slow in helical pitch which is carried out at Step C 4 , is slow 0.2 or so in helical pitch, and the dose of X-rays radiated to the subject was greater than at the normal scan.
- the joining portions of the X-ray projection data are caused to overlap each other in such a manner that the joining portions thereof become preferably smooth.
- the X-ray projection data on both side of the joining portion is multiplied by a weight coefficient to make weighted addition, thereby combining the X-ray projection data. Since, however, the X-ray projection data different in time and cardiac period or heartbeat are combined, the discontinuity in joining portion cannot be resolved even this unless reproducibility of body motion of the subject is obtained, so artifacts on the tomographic image and banding artifacts at the three-dimensional image display cannot be avoided.
- FIG. 23 shows a flowchart for describing cardiac photography or imaging in the first embodiment.
- the cardiac imaging of the first embodiment will be explained with reference to the figure.
- a scan width of one example, a gantry rotational speed, and a helical pitch for a high-pitch helical scan are assumed to be 40 mm, 0.35 seconds per rotation and 1.375 respectively in the following description.
- the helical pitch indicates a ratio S/D between a z-direction width D of an X-ray beam and the amount S of subject's motion per rotation of an X-ray data acquisition system.
- the electrocardiograph 31 is mounted to the subject to acquire or collect an electrocardiographic signal.
- an imaging range is designated by a scout image obtained by a scout scan for the subject, and a cardiac area of the scout image is designated.
- the resultant scout image is displayed on the display screen R of FIG. 14 , and a cardiac position is designated.
- an operator sets a scan range for a subsequent helical scan and an image reconstruction range.
- a low dosage-based high-speed helical scan large in helical pitch is performed at such a timing that, for example, a cardiac phase of 75 ⁇ 5% of a cardiac period P or a cardiac phase of a cardiac period P+0.5 seconds is placed in a z-direction central position of an imaging range for the helical scan as a predetermined cardiac phase while electrocardiographic waveforms are being observed.
- the helical scan at Step S 13 and the image reconstruction at Step S 14 subsequent to Step S 13 intend to photograph or image portions or regions clearly undisplayed at the scout photography at a low dosage, perform image reconstruction at high speed, and confirm the condition for imaging or photographing a cardiac portion or region. They are not necessarily essential.
- the helical scan at Step S 13 may preferably be performed using a high-speed helical scan large in helical pitch and its method to be performed at Step S 17 to be described later. This is not necessarily required so. At least, the helical scan at Step 13 will be performed to confirm whether the present apparatus detects a proper cardiac phase and photograph or image a proper phase corresponding to the cardiac phase, by using the low-dosage scan at Step S 13 and the image reconstruction.
- Step S 14 sectional conversion images of a cardiac coronal plane and/or its sagittal plane are image-reconstructed using the X-ray projection data acquired at Step S 13 .
- Confirmation is made as to whether the heart is placed in a predetermined cardiac phase (mesodiastole or predetermined cardiac triggered phase).
- confirmation is made as to whether each part of the heart such as the coronary artery is properly drawn or plotted at the coronal image and sagittal image. It is also determined whether imaging is done in the proper cardiac phase or cardiac triggered phase. Further, a decision is made as to whether the imaging is done in the proper cardiac phase or cardiac triggered phase, depending upon the degree of artifacts produced from the motion of the heart.
- a contrast agent (iodide) is injected into an arm vein of the subject in small quantities.
- the cardiac region (main e or the like) of the subject is monitor-scanned by an intermittent scan after the elapse of a predetermined time having considered allowance prior to cardiac attainment.
- a delay time (that is, a delay time from the injection of the contrast agent to its attainment to the main art) from image reconstruction in real time to the attainment of a CT value of a vascular portion to a predetermined value or more is determined.
- a low exposed dose is realized by performing a conventional scan (axial scan) of one rotation (0.35 s) of gantry at approximately one-second intervals.
- a monitor scan corresponding to an intermittent scan at time T 1 intervals is shown in FIG. 25 .
- Step S 16 When it is found at Step S 16 that the proper cardiac phase or cardiac triggered phase is taken by reference to the result of discrimination at Step S 14 , a routine procedure for the cardiac imaging proceeds to Step S 17 , where an actual injection of the contrast agent is performed again and a high-speed helical scan (actual scan) large in helical pitch is performed in timing with the predetermined cardiac phase subsequent to the elapse of the measured delay time.
- a high-speed helical scan actual scan
- FIG. 25 shows the relationship between a helical scan for an actual scan and a cardiac periodic signal.
- Step S 15 the subject is returned to the predetermined position after the acquisition of the delay time, and the contrast agent is injected into the arm's vein. Further, the elapse of a contrast agent delay time is awaited. When the delay time is almost reached, the high-speed helical scan large in helical pitch is effected on the subject. The subject is conveyed to the scan start position zs by the cradle 12 .
- the waiting time Tw is awaited from the cardiac periodic signal tr 1 at the X-ray data acquisition start time tss and X-ray irradiation is started, after which a high-speed helical scan large in helical pitch is performed.
- a cardiac region of 12 cm is helically scanned where the scan speed is 0.35 seconds per rotation, the X-ray beam width is 40 mm, and the helical pitch is 1.375
- the imaging of the whole heart is allowed at approximately one heartbeat or time not greater than it, and hence a high-speed scan can be realized.
- Step S 18 an electrocardiographic synchronism-based helical scan slow in helical pitch similar to the prior art is performed. Preparing this scan method is effective for a subject high in heart rate.
- relative velocity of the subject to the data acquisition system at the helical scan is shown in graph form shown below FIG. 25 . It is better that the cradle should be operated at the maximum velocity between [tss and tse] corresponding to the X-ray data acquisition range Ts. Therefore, a run-up time and a run-up distance for acceleration are determined in advance, and then the operating speed of the cradle 12 is controlled so as to reach the maximum or top velocity V 1 at the time tss. When the scan gantry 20 is operated, the operating speed of the scan gantry 20 is controlled.
- FIG. 26 In view of processing for arrhythmia, the relationship between a helical scan and an electrocardiographic sync signal at the time that a cardiac or heartbeat period is made long is shown in FIG. 26 , and the relationship between a helical scan and an electrocardiographic sync signal at the time that a cardiac period is made short is shown in FIG. 27 .
- the cardiac period is abnormal at the time of tw where a trigger signal of an electrocardiographic sync signal does not come by the time tw corresponding to 120% of the average cardiac period Th.
- the cardiac period is abnormal at the time of tw where a trigger signal of an electrocardiographic sync signal comes by the time tw corresponding to 80% of the average cardiac period Th.
- X-ray radiation will be made stopped if possible. If it is unable to stop the X-ray radiation, X-ray projection data acquisition is performed to the end of the helical scan. In any case, the start and end points of the helical scan are reversed from this time and re-imaging can be performed again in the opposite direction. However, if arrhythmia appears seriously and the cardiac period is not stable, then the imaging can also be stopped.
- a second embodiment shows an embodiment of a method illustrative of the contrast agent synchronous imaging employed in Step S 15 or Step S 17 shown in FIG. 23 of the first embodiment
- FIG. 28 shows an example of the flow of processing for the contrast agent synchronous imaging.
- Step C 1 a subject is placed on the cradle 12 and they are aligned with each other.
- Step C 2 scout image acquisition is performed.
- Step C 3 an imaging condition setting is carried out.
- Step C 4 baseline tomographic image imaging is performed.
- Step C 5 a baseline tomographic image display is done.
- Step C 6 a contrast agent synchronous imaging condition setting is carried out.
- a region-of-interest setting on a baseline tomographic image is carried out.
- Step C 7 a monitor scan is started.
- the monitor scan is shown in FIG. 29 .
- Step C 8 it is decided whether an average CT value in the region of interest exceeds a set threshold value. If the answer is found to be YES, then the flow of processing proceeds to Step C 9 . If the answer is found to be NO, then Step C 8 is repeated. A delay time for the contrast agent is found from the timing at which the average CT value exceeds the threshold value.
- Step C 9 preparation for an actual scan is made.
- the cradle 12 on the photographing table 10 is shifted to the position for the actual scan.
- Step C 11 an actual scan tomographic image display is carried out.
- the region of interest used in the monitor scan is set. If a plurality of sheets of tomographic images are photographed in the z direction at the monitor scan, then a plurality of sheets of tomographic images are photographed in the z direction even at the baseline tomographic image photography. When a plurality of regions of interest are set in the z direction, a plurality of regions of interest are set in the z direction even at the baseline tomographic image photography. If a plurality of regions of interest are set within a tomographic image in an xy plane, then a plurality of regions of interest are set to within one tomographic image at the baseline tomographic image photography.
- a region of interest 1 is set to a man artery. Tis device that a contrast agent flows and the region of interest is first set to such a main artery that a CT value increases, thereby using it as a trigger for the actual scan. A change in CT value of each region of interest ROI 1 at each time t is shown in FIG. 30( b ).
- a threshold value used as for a trigger for the actual scan is set to a CT value 100 on the region of interest 1 (ROI 1 )
- a CT value on the region of interest 1 (ROI 1 ) reaches a predetermined threshold value in a little less than about 30 seconds, so that the actual scan is triggered.
- the actual scan is triggered in this way.
- Step S 15 a contrast agent delay time is outputted or displayed upon a test injection.
- the imaging or photographing time can greatly be shortened by the high-speed helical scan, and the exposed dosage can greatly be reduced (to 1 ⁇ 5 of the conventional one). Further, a reduction in the amount of injection of the contrast agent can also be expected.
- the present embodiment results in a technology essential as one heart imaging or scanning technique by an X-ray CT apparatus using a future multi-row X-ray detector or two-dimensional X-ray area detector of a matrix structure typified by a flat panel X-ray detector.
- the above-described X-ray CT apparatus 100 can bring about an advantageous effect in that it is possible to realize the photography or imaging of the heart at the low dosage and high speed and with good image quality by the helical scan, variable pitch helical scan or helical shuttle scan of the X-ray CT apparatus having the multi-row X-ray deter or the two -dimensional X-ray area detector of matrix structure typified by the flat panel X-ray detector.
- the image reconstructing method according to the present embodiment may be a three-dimensional image reconstructing method based on the Feldkamp method known to date. Further, it may be another three-dimensional image reconstructing method. Alternatively, it may be two-dimensional image reconstruction.
- the present invention is not limited to it.
- the two coronary arteries for feeding nutrition to the heart muscle extend over the surface of the heart.
- the coronary arteries move greatly with the motion of the heart at the surface of the heart. Therefore, artifacts with the motion thereof are apt to occur in its tomographic image. Accordingly, the present invention brings about an effect even with resect to the photography of the coronary arteries in particular in like manner.
- the present invention can be applied even to such an X-ray CT apparatus that the scan gantry 20 is moved in the direction of the body axis of the subject in reverse.
- the row-direction (z-direction) filters different in coefficient for every row are convoluted, thereby adjusting variations in image quality and realizing a uniform slice thickness, artifacts and the image quality of noise at each row.
- various z-direction filter coefficients are however considered therefor, any can bring about a similar effect.
Abstract
Description
[Equation 1]
D11(view,j,i)=D1(view,j,i)•(Bo(j,i)+B 1(j,i)•D1(view,j,i)+B 2(j,i)•D1(view,j,i)2) (1)
[Equation 2]
(w1(i), w2(i), w3(i), w4(i), w5(i)) (2)
[Equation 5]
D11(view,−1,i)=D11(view,0,i)=D11(view,1,i) (5)
[Equation 6]
D11(view,ROW,i)=D11(view,ROW+1,i)=D11(view,ROW+2,i) (6)
[Equation 7]
D13(view,j,i)=D12(view,j,i)*Kernel(j) (7)
[Equation 8]
D32(x,y,z)=D31(x,y,z)*Filter(z) (8)
[Equation 10]
v(−l), v(−l+1), . . . v(−l), v(0), v(l−1), v(l) (10)
[Equation 11]
βb=βa+180°−2γ (11)
[Equation 12]
D2(0,x,y)=(ωa•D2(0,x,y)— a+ωb•D2(0,x,y)— b (12)
[Equation 13]
ωa+ωb=1 (13)
[Equation 14]
ga=f(γmax, αa, βa) (14)
[Equation 15]
gb=f(γmax, αb, βb) (15)
[Equation 16]
xa=2·ga q/(ga q +gb q) (16)
[Equation 17]
xb=2·gb q/(ga q +gb q) (17)
[Equation 18]
wa=xa 2·(3−2xa) (18)
[Equation 19]
wb=xb 2·(3−2xb) (19)
(For instance, q=1)
[Equation 20]
ga=max[0, {(π/2+γmax)−|βα|}]·|tan(αa)| (20)
[Equation 21]
gb=max[0, {(π/2+γmax)−|βb|}]·tan(αb)| (21)
- (1) Data acquisition is performed by a one helical scan continuous in a time direction as a countermeasure for the absence of the reproducibility of the subject's body motion.
- (2) Three-dimensional image reconstruction is used in which artifacts are less reduced even though a high-speed helical scan large in helical pitch is performed.
- (3) The conventional cardiac imaging method is usable when the cardiac period is short.
[Equation 22]
tc=(tss+tse)/2=(trs+tre)/2 (22)
[Equation 23]
trs=tc−Tr/2=tss+T1 (23)
[Equation 24]
tss=tc−Ts/2=trs−T1 (24)
[Equation 25]
Tw=Th+tc−Ts/2 (25)
Claims (18)
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Also Published As
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US20070237286A1 (en) | 2007-10-11 |
KR20070100178A (en) | 2007-10-10 |
JP2007275314A (en) | 2007-10-25 |
NL1033652C2 (en) | 2008-12-15 |
DE102007017979A1 (en) | 2007-10-11 |
NL1033652A1 (en) | 2007-10-09 |
CN101049243B (en) | 2011-01-26 |
JP4495109B2 (en) | 2010-06-30 |
CN101049243A (en) | 2007-10-10 |
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